Branch prediction instructions having mask values involving unloading and loading branch history data

a branch history and mask value technology, applied in the field of branch prediction methods, can solve the problems of pipeline drain, severe penalty for bht errors, and errors in branch prediction, and achieve the effect of saving data

Inactive Publication Date: 2012-03-06
INT BUSINESS MASCH CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

This approach reduces the hardware requirements for branch prediction, improves prediction accuracy, and enhances processor performance by prefetching relevant branch information ahead of its use, minimizing pipeline bubbles and increasing the prefetching accuracy.

Problems solved by technology

Branch prediction errors occur when the table is incorrect.
Branch prediction accuracy may reach 80 to 90 percent, but there is a severe penalty when the BHT is incorrect.
Prediction errors may cause the processor pipeline to be flushed, causing pipeline drain.

Method used

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  • Branch prediction instructions having mask values involving unloading and loading branch history data
  • Branch prediction instructions having mask values involving unloading and loading branch history data
  • Branch prediction instructions having mask values involving unloading and loading branch history data

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Embodiment Construction

[0023]Methods involving prefetching into a branch prediction mechanism are provided.

[0024]In this regard, it is desirable to reduce the size of a branch history table (BHT) size while improving branch prediction accuracy and processor performance. To accomplish this, a mechanism is described that allows future branch information to be prefetched into the BHT.

[0025]Prefetching future branch information into a prefetched branch history table (PBHT) allows a designer to reduce the size of the BHT without sacrificing branch prediction accuracy or performance. The branch information used to process the upcoming (future) instructions and branches of a program is held in the speed critical area (PBHT), while the full program and branch information are maintained in program save areas or main memory. The full size of the branch prediction mechanism is no longer limited in size by the hardware or cycle time considerations. The size of the PBHT need only by limited to the amount of branch inf...

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Abstract

A method for branch prediction, the method comprising, receiving a load instruction including a first data location in a first memory area, retrieving data including a branch address and a target address from the first data location, and saving the data in a branch prediction memory, or receiving an unload instruction including the first data location in the first memory area, retrieving data including a branch address and a target address from the branch prediction memory, and saving the data in the first data location.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates generally to computer processing techniques and, more particularly, to methods involving branch prediction in computer processing.[0003]2. Description of Background[0004]Branch prediction is used to improve the performance of processors. When a processor detects a conditional branch, an uncertainty is temporarily introduced into the processor pipeline. If the branch is taken, the next instruction is fetched from an address usually specified in the branch instruction. If the branch is not taken, execution proceeds to the instruction following the branch.[0005]Large amounts of chip area are dedicated to the processor branch prediction mechanism. In practice, the branch address and target address of each branch encountered by the processor are saved in a table, called a Branch History Table (BHT). During the instruction fetch phase of a processor pipeline, the BHT is searched for a matching branch ad...

Claims

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Application Information

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Patent Type & AuthorityPatents(United States)
IPC IPC(8): G06F9/312
CPCG06F9/3005G06F9/30076G06F9/3806G06F9/3844G06F9/323
InventorEMMA, PHILIP G.HARTSTEIN, ALLAN M.LANGSTON, KEITH N.PRASKY, BRIAN R.PUZAK, THOMAS R.WEBB, CHARLES F.
OwnerINT BUSINESS MASCH CORP